The Experts below are selected from a list of 15435 Experts worldwide ranked by ideXlab platform
Ephraim Suhir - One of the best experts on this subject based on the ideXlab platform.
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Minimizing thermally induced interfacial Shearing Stress in a thermoelectric module
2012Co-Authors: Amirkoushyar Ziabari, Ephraim Suhir, Ali ShakouriAbstract:The problem of minimizing the level of the thermally induced interfacial Shearing Stress in a Thermo-Electric Module (TEM) is addressed using analytical and finite-element-analysis (FEA) based modeling. The maximum Stress is calculated for different leg sizes. Good agreement between the analytical and FEA predictions has been found. It is concluded that the Shearing Stress can be effectively minimized by using thinner legs with compliant interfaces.
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Bending of a bi-material cantilever beam, with consideration of the role of the interfacial Shearing Stress
ZAMM - Journal of Applied Mathematics and Mechanics Zeitschrift für Angewandte Mathematik und Mechanik, 2012Co-Authors: Ephraim Suhir, Johann NicolicsAbstract:A simple, easy-to-use and physically meaningful analytical (“mathematical”) model for the prediction of the interfacial Shearing Stress in, and the maximum bow of, a bi-material cantilever beam is developed. The beam experiences bending under the action of a lateral concentrated force applied to its free end. It is shown that the effect of the longitudinal interfacial compliance of the beam should be considered for short beams with not-very-stiff interfaces.
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Transient thermomechanical study of a thick-wire bond with particular attention to the interfacial Shearing Stress
2012 35th International Spring Seminar on Electronics Technology, 2012Co-Authors: Bernhard Nagl, Ephraim Suhir, Walter Gschohsmann, Johann NicolicsAbstract:A high-power IGBT (Isolated Gate Bipolar Transistor) module has been thermomechanically analyzed in the moment of switching on short circuit. We studied the extremely rapidly changing temperature distribution within a wire bond by a transient thermal simulation on the basis of an experimentally determined power loss as function of time, a finite element simulation of thermomechanically induced Stress and strain distribution within the bond-wire wedge and the silicon chip, and a simple but meaningful analytical model of the same arrangement, with special attention to the interfacial Shearing Stress as function of time. The analyses revealed a surprising result: during the first few microseconds the extremely high power loss density in the silicon chip causes a rapid temperature increase and expansion of the silicon chip which leads to a tensile Stress in the aluminum bond wire, whereas in the consecutive phase the temperature of the aluminum wire approaches the one of the chip, whereby the aluminum wire turns to compressive Stress which means a reversal of shear Stress at the wire/chip interface. This could be a new explanation for the field failures known.
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Approximate evaluation of the interfacial Shearing Stress in cylindrical double lap shear joints with application to dual-coated optical fibers
International Journal of Solids and Structures, 1994Co-Authors: Ephraim SuhirAbstract:Abstract A simplified analytical model is developed for the evaluation of the interfacial Shearing Stress in a cylindrical double lap shear joint, with application to dual-coated optical fiber specimens subjected to pull-out testing, in situ measurements of Young's (shear) modulus of the primary coating material, and stripping of the coating from the glass. The objective of the analysis is to assess the effect of the material properties and specimen's geometry on the magnitude and distribution of the Shearing Stress. It is shown that the longitudinal distribution of this Stress is nonuniform and that, for the given specimen's length, its maximum value increases with a decrease in the thickness of the primary coating. As far as the pull-out testing and Young's modulus evaluations are concerned, it is concluded that, while 1 cm long specimens with approximately 30 μm thick primary coating (such specimens are currently used in pull-out tests) are acceptable, shorter specimens will result in a more uniform Stress distribution and, as a consequence of that, in more stable experimental data. As to the coating strippability, it is desirable that the stripping area be short, although satisfactory strippability is often achieved even for long stripping areas. It is concluded that a multiblade stripping tool might be worthwhile to consider if long portions of coating have to be removed from the fiber. The obtained results can be useful for comparing the adhesive strength of the primary coating in fibers of different lengths and with different coating designs, for the in situ evaluation of Young's modulus of the primary coating material from the measured axial displacement of the glass fiber, and for the assessment of the effect of material properties and fiber geometry on the strippability of the fiber coating.
E Suhir - One of the best experts on this subject based on the ideXlab platform.
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minimizing thermally induced interfacial Shearing Stress in a thermoelectric module with low fractional area coverage
Microelectronics Journal, 2014Co-Authors: Amirkoushyar Ziabari, E Suhir, Ali ShakouriAbstract:High temperature differences between the ceramic parts in thermo-electric modules (TEMs) intended for high temperature applications makes the TEMs vulnerable to the elevated thermal Stress leading to possible structural (mechanical) failures. The problem of reducing the interfacial Shearing Stress in a TEM structure is addressed using analytical and finite-element-analysis (FEA) modeling. The maximum Shearing Stress occurring at the ends of the peripheral legs (and supposedly responsible for the structural robustness of the assembly) is calculated for different leg sizes. Good agreement between the analytical and FEA predictions has been found. It is concluded that the Shearing Stress can be effectively reduced by using thinner (smaller fractional area coverage) and longer (in the through thickness direction of the module) legs and compliant interfacial materials.
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assembly bonded at the ends could thinner and longer legs result in a lower thermal Stress in a thermoelectric module design
Journal of Applied Mechanics, 2012Co-Authors: E Suhir, Ali ShakouriAbstract:An analytical (mathematical) thermal Stress model has been developed for an electronic assembly comprised of identical components bonded at their end portions and subjected to different temperatures. The model is used to assess the effect of the size (dimension in the x-direction) and compliance of the bonded regions (legs) on the maximum interfacial Shearing Stress that is supposedly responsible for the mechanical robustness of the assembly. The numerical example is carried out for a simplified two-legged Bismuth-Telluride-Alloy (BTA)-based thermoelectric module (TEM) design. It has been determined that thinner (dimension in the horizontal, x-direction) and longer (dimension in the vertical, y-direction) bonds (legs) could result in a considerable relief in the interfacial Stress. In the numerical example carried out for a 10 mm long (dimension in the x-direction) TEM assembly with two peripheral 1 mm thick (dimension in the x-direction) legs, the predicted maximum interfacial Shearing Stress is only about 40% of the maximum Stress in the corresponding homogeneously bonded assembly, when the bond occupies the entire interface between the assembly components. It has been determined also that if thickand-short legs are employed, the maximum interfacial Shearing Stress might not be very much different from the Stress in a homogeneously bonded assembly, so that there is no need, as far as physical design and robustness of the assembly is concerned, to use a homogeneous bond or a multileg system. The application of such a system might be needed, however, for the satisfactory functional (thermo-electrical) performance of the device. In any event, it is imperative that sufficient bonding strength is assured in the assembly. If very thin legs are considered for lower Stresses, the minimum acceptable size (real estate) of the interfaces (in the horizontal plane) should be experimentally determined (say, by shear-off testing) so that this strength is not compromised. On the other hand, owing to a lower Stress level in an assembly with thin-and-long legs, assurance of its interfacial strength is less of a challenge than for an assembly with a homogeneous bond or with stiff thick-and-short legs. The obtained results could be used particularly for considering, based on the suggested predictive model, an alternative to the existing TEM designs, which are characterized by multiple big (thick-and-long) legs. In our novel design, fewer small (thin-and-short) legs could be employed, so that the size and thickness of the TEM is reduced for the acceptable Stress level. [DOI: 10.1115/1.4006597]
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Interfacial Shearing Stress in pull-out testing of dual-coated lightguide specimens
Journal of Lightwave Technology, 1993Co-Authors: E SuhirAbstract:A simple analytical model is developed for the evaluation of the interfacial Shearing Stress at the glass fiber surface in dual-coated optical fiber specimen subjected to tension. It is shown that the distribution of this Stress is nonuniform and that, for the given specimen's length, its maximum value increases with a decrease in the thickness of the primary coating. The obtained results can be useful for comparing the adhesive strength of the primary coating material in fibers of different lengths and with different coating designs, as well as for the in situ evaluation of Young's (shear) modulus of this material from the measured axial displacement of the glass fiber.
Ali Shakouri - One of the best experts on this subject based on the ideXlab platform.
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minimizing thermally induced interfacial Shearing Stress in a thermoelectric module with low fractional area coverage
Microelectronics Journal, 2014Co-Authors: Amirkoushyar Ziabari, E Suhir, Ali ShakouriAbstract:High temperature differences between the ceramic parts in thermo-electric modules (TEMs) intended for high temperature applications makes the TEMs vulnerable to the elevated thermal Stress leading to possible structural (mechanical) failures. The problem of reducing the interfacial Shearing Stress in a TEM structure is addressed using analytical and finite-element-analysis (FEA) modeling. The maximum Shearing Stress occurring at the ends of the peripheral legs (and supposedly responsible for the structural robustness of the assembly) is calculated for different leg sizes. Good agreement between the analytical and FEA predictions has been found. It is concluded that the Shearing Stress can be effectively reduced by using thinner (smaller fractional area coverage) and longer (in the through thickness direction of the module) legs and compliant interfacial materials.
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assembly bonded at the ends could thinner and longer legs result in a lower thermal Stress in a thermoelectric module design
Journal of Applied Mechanics, 2012Co-Authors: E Suhir, Ali ShakouriAbstract:An analytical (mathematical) thermal Stress model has been developed for an electronic assembly comprised of identical components bonded at their end portions and subjected to different temperatures. The model is used to assess the effect of the size (dimension in the x-direction) and compliance of the bonded regions (legs) on the maximum interfacial Shearing Stress that is supposedly responsible for the mechanical robustness of the assembly. The numerical example is carried out for a simplified two-legged Bismuth-Telluride-Alloy (BTA)-based thermoelectric module (TEM) design. It has been determined that thinner (dimension in the horizontal, x-direction) and longer (dimension in the vertical, y-direction) bonds (legs) could result in a considerable relief in the interfacial Stress. In the numerical example carried out for a 10 mm long (dimension in the x-direction) TEM assembly with two peripheral 1 mm thick (dimension in the x-direction) legs, the predicted maximum interfacial Shearing Stress is only about 40% of the maximum Stress in the corresponding homogeneously bonded assembly, when the bond occupies the entire interface between the assembly components. It has been determined also that if thickand-short legs are employed, the maximum interfacial Shearing Stress might not be very much different from the Stress in a homogeneously bonded assembly, so that there is no need, as far as physical design and robustness of the assembly is concerned, to use a homogeneous bond or a multileg system. The application of such a system might be needed, however, for the satisfactory functional (thermo-electrical) performance of the device. In any event, it is imperative that sufficient bonding strength is assured in the assembly. If very thin legs are considered for lower Stresses, the minimum acceptable size (real estate) of the interfaces (in the horizontal plane) should be experimentally determined (say, by shear-off testing) so that this strength is not compromised. On the other hand, owing to a lower Stress level in an assembly with thin-and-long legs, assurance of its interfacial strength is less of a challenge than for an assembly with a homogeneous bond or with stiff thick-and-short legs. The obtained results could be used particularly for considering, based on the suggested predictive model, an alternative to the existing TEM designs, which are characterized by multiple big (thick-and-long) legs. In our novel design, fewer small (thin-and-short) legs could be employed, so that the size and thickness of the TEM is reduced for the acceptable Stress level. [DOI: 10.1115/1.4006597]
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Minimizing thermally induced interfacial Shearing Stress in a thermoelectric module
2012Co-Authors: Amirkoushyar Ziabari, Ephraim Suhir, Ali ShakouriAbstract:The problem of minimizing the level of the thermally induced interfacial Shearing Stress in a Thermo-Electric Module (TEM) is addressed using analytical and finite-element-analysis (FEA) based modeling. The maximum Stress is calculated for different leg sizes. Good agreement between the analytical and FEA predictions has been found. It is concluded that the Shearing Stress can be effectively minimized by using thinner legs with compliant interfaces.
S Nadeem - One of the best experts on this subject based on the ideXlab platform.
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a mathematical study of non newtonian micropolar fluid in arterial blood flow through composite stenosis
Applied Mathematics & Information Sciences, 2014Co-Authors: R Ellahi, S Nadeem, S U Rahman, Mudassar M Gulzar, Kambiz VafaiAbstract:The unsteady and incompressible flow of non-Newtonian fluid through co mposite stenosis is investigated in the present study. The micropolar fluid is treated as a blood flow model. Mild stenosis and slip velocity are also taken into account. The governing equations are given in cylindrical coordinates system. Analytic solutions o f velocity and volumetric flow flux are developed interms of modified Bessel functions. The expressions for the impedance (flow r esistance) λ, the wall shear Stress distribution in the stenotic region Tw and the Shearing Stress at the stenosis throat Ts are also given. Impact of involved pertinent parameters is sketched and examined by the resistance of impedance and shear Stress. The stream lines are also made for different sundry parameters.
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simulation of variable viscosity and jeffrey fluid model for blood flow through a tapered artery with a stenosis
Communications in Theoretical Physics, 2012Co-Authors: Noreen Sher Akbar, S NadeemAbstract:Non-Newtonian fluid model for blood flow through a tapered artery with a stenosis and variable viscosity by modeling blood as Jeffrey fluid has been studied in this paper. The Jeffrey fluid has two parameters, the relaxation time λ1 and retardation time λ2. The governing equations are simplified using the case of mild stenosis. Perturbation method is used to solve the resulting equations. The effects of non-Newtonian nature of blood on velocity profile, temperature profile, wall shear Stress, Shearing Stress at the stenotsis throat and impedance of the artery are discussed. The results for Newtonian fluid are obtained as special case from this model.
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power law fluid model for blood flow through a tapered artery with a stenosis
Applied Mathematics and Computation, 2011Co-Authors: S Nadeem, Noreen Sher Akbar, Awatif A. HendiAbstract:Abstract In the present paper, blood flow through a tapered artery with a stenosis is analyzed, assuming the flow is steady and blood is treated as non-Newtonian power law fluid model. Exact solution has been evaluated for velocity, resistance impedance, wall shear Stress and Shearing Stress at the stenosis throat. The graphical results of different types of tapered arteries (i.e. converging tapering, diverging tapering, non-tapered artery) have been examined for different parameters of interest. Some special cases of the problem are also presented.
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simulation of heat and chemical reactions on reiner rivlin fluid model for blood flow through a tapered artery with a stenosis
Heat and Mass Transfer, 2010Co-Authors: Noreen Sher Akbar, S NadeemAbstract:In the present article, we have analyzed the effects of heat and mass transfer on Reiner Rivlin fluid model for blood flow through a tapered artery with a stenosis. The constitutive equations for a Reiner Rivlin fluid have been modelled in cylindrical coordinates. A perturbation series in dimensionless Reiner Rivlin fluid parameter (λ1 ≪ 1) have been used to obtain explicit forms for the velocity, temperature, concentration, resistance impedance, wall shear Stress and Shearing Stress at the stenosis throat. The graphical results of different type of tapered arteries i.e. converging tapering, diverging tapering, non-tapered artery have been examined for different parameters of interest.
Youhe Zhou - One of the best experts on this subject based on the ideXlab platform.
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flux pinning induced interfacial Shearing and transverse normal Stress in a superconducting coated conductor long strip
Journal of Applied Physics, 2012Co-Authors: Ze Jing, Huadong Yong, Youhe ZhouAbstract:In this paper, a theoretical model is proposed to analyze the transverse normal Stress and interfacial Shearing Stress induced by the electromagnetic force in the superconducting coated conductor. The plane strain approach is used and a singular integral equation is derived. By assuming that the critical current density is magnetic field independent and the superconducting film is infinitely thin, the interfacial Shearing Stress and normal Stress in the film are evaluated for the coated conductor during the increasing and decreasing in the transport current, respectively. The calculation results are discussed and compared for the conductor with different substrate and geometry. The results indicate that the coated conductor with stiffer substrate and larger width experiences larger interfacial Shearing Stress and less normal Stress in the film.
